Essential features that serve to distinguish malignant cells from their normal counterparts include their ability to proliferate independently of normal regulatory mechanisms, invade normal tissue and metastasize. Increasing evidence suggests that these characteristics may be modulated by the tumor cell's nucleus and surface membranes. Colorectal cancer is a leading cause of death among adult patients with internal malignancies and is incurable in approximately one-half of the patients at the time of initial diagnosis. In the past two decades, cure rates of the disease have stayed approximately the same. Elucidation of the surface membrane and intracellular events that occur during normal differentiation, those altered leading to an occurring during malignant transformation as well as better methods for the early detection of this disease are clearly needed and are the overall goals of this proposal. To achieve these goals, proliferative and non-proliferative colonic epithelial cells will first be isolated from the proximal and distal rat colon. Lumenal and contralumenal plasma membranes will then be isolated from these cells. Each of these membranes will be characterized during normal differentiation with respect to: 1) phospholipid/neutral lipid composition; 2) phospholipid/neutral lipid turnover and biosynthesis; 3) membrane lipid "fluidity" and protein-lipid interactions; 4) amiloride-sensitive Na+/H+ exchange; and 5) glycosphingolipid composition and biosynthesis. After this is accomplished in the "normal" rat colon, animals will be treated with either the procarcinogen 1,2 dimethylhydrazine (DMH) or the direct carcinogen N-methyl-N'-nitro-N-nitroguadinine (MNNG) for 5, 10 or 15 weeks, i.e., prior to the development of overt colonic tumors. Colonic antipodal plasma membranes will then be isolated from proximal and distal colonocytes and their biochemical parameters (see above) analyzed. Differences in these parameters between "normal" and carcinogen-treated membranes may be useful in detecting early or "premalignant" changes. These differences might also prove useful in increasing our understanding of the malignant transformation process.